After more than a decade of planning, Nelson Dam is about to be removed.
Work scheduled for this week includes installing a cofferdam, which is a temporary structure that allows a work area to be dewatered. In addition, this week sections of the riverbed and flood plain are scheduled to be excavated to ensure new paths for the Naches River during construction. These sections will be filled in and re-contoured later in the project. Both of these projects are expected to take about 10 days to complete.
Work over the next month will also include installing a temporary bridge to get equipment, material and personnel in and out of the dewatered area, installing a cofferdam for heavy equipment access, and continued de-watering of the work area.
It is estimated that demolishing Nelson Dam will begin the week of September 20th.
All dates are approximate. The timeline may shift based on weather, equipment and other factors.
When complete, the project will replace Nelson Dam to improve fish passage and water supply reliability.
Nelson Dam, on the Naches tributary of the Yakima River, was built in the 1920s to divert irrigation water for Yakima and the Naches-Cowiche Irrigation Association. The original design did not allow any fish passage.
The dam has held back tons of sediment and silt over the years, raising the river bed and causing the Naches River to overflow its banks and move into the surrounding community during even minor flooding.
The project will improve fish passage and sediment continuity to improve habitat, increase flow conveyance to decrease flooding risks for nearby landowners, and improve water supply reliability.
The City of Yakima and Yakima County have been collaborating on the design and implementation of this project. The dam removal and replacement is one of several major public works projects initiated by the Yakima Basin Integrated Plan.
The City of Yakima is investing $10.8 million in the $26 million multi-agency collaboration — part of the Yakima Basin Integrated Plan — over the next four to five years.
The City of Yakima received $4.4 million from the Washington State Floodplain by Design program, about $4.1 million from Brian Abbott Fish Barrier Removal Board, and just over $1.3 million from the state’s Capital Budget for the Nelson Dam project. The City continues to seek additional funding from state and federal sources to complete the project.
For more about the project, contact City of Yakima Assistant Public Works Director Dave Brown by phone at 509-575-6154 or by email at David.Brown@yakimawa.gov